Jeg går ikke i seng, før jeg har læst det sidste kapitel i min roman.

Because this is a main clause, and Danish main clauses normally follow the V2 rule: the finite verb comes in second position.

So the structure is:

• Jeg = subject
• går = finite verb
• ikke = negation

That gives Jeg går ikke ...

This is different from English, where not usually comes after an auxiliary: I do not go. In Danish, if there is no auxiliary, ikke usually comes after the finite verb in a main clause.

Gå i seng is a fixed expression meaning to go to bed.

A few important points:

• gå literally means go / walk
• i seng is idiomatic and means to bed
• there is no article, just as English says go to bed, not usually go to the bed

So jeg går i seng is the normal way to say I go to bed or I’m going to bed.

You should learn gå i seng as a chunk.

Danish very often uses the present tense for future meaning when the context already makes the time clear.

So Jeg går ikke i seng, før ... can refer to what the speaker intends to do later, even though går is present tense.

This is very common in Danish. English does something similar sometimes:

• I’m not going to bed until ...
• I leave tomorrow

If you want, Danish can also use vil for future meaning, but it is not necessary here.

Yes — in English, a negative main clause often uses until:

• I’m not going to bed until ...

But Danish commonly uses ikke ... før in exactly this kind of sentence.

So:

• Jeg går ikke i seng, før ...

is a very standard Danish pattern.

Literally, før means before, but in a sentence with ikke, the whole structure often matches English not ... until.

Har læst is the present perfect.

It is used here because the reading must be completed before the speaker goes to bed. The sentence is not just about reading in general; it is about finishing that chapter first.

So the idea is:

• first: the reading is completed
• then: going to bed happens

That is why har læst works well here.

Also:

• har = present tense of have
• læst = past participle of læse (to read)

Because før jeg har læst ... is a subordinate clause.

In Danish subordinate clauses, the word order is usually:

• conjunction
• subject
• finite verb
• other elements

So:

• før = conjunction
• jeg = subject
• har = finite verb
• læst = past participle

That gives før jeg har læst ...

The V2 rule does not apply inside this subordinate clause.

Because when a noun is definite and has an adjective before it, standard Danish normally uses:

• definite article
• adjective
• noun in its basic form

So:

• det sidste kapitel = the last chapter

Here:

• det is the definite article for a neuter noun
• sidste is the adjective
• kapitel stays in its basic form

Compare:

• kapitel = chapter
• kapitlet = the chapter
• det sidste kapitel = the last chapter

So once the adjective is there, you use det ... kapitel, not kapitlet.

Because sidste is the form used before a noun.

Here it describes kapitel, so you need the adjectival form:

• det sidste kapitel

Sidst is usually an adverb, meaning something like last or lastly in a different grammatical role, for example:

• Jeg så ham sidst i går = I saw him last yesterday / most recently yesterday

So in front of a noun, use sidste, not sidst.

Here i is the natural preposition because a chapter is understood as something inside a book.

So det sidste kapitel i min roman means the last chapter in my novel.

In English, you might also say of my novel, but Danish often prefers i in this kind of context.

Also, min roman can depend on context:

• the novel I own
• the novel I am reading
• the novel I am writing

The grammar itself does not tell you which one; context does.

Yes, you could.

That version is also natural, but it adds a slightly different feel:

• Jeg går ikke i seng, før ... = a plain statement about what will happen / what the speaker does
• Jeg vil ikke gå i seng, før ... = can sound a bit more like intention, willingness, or determination

So both are possible, but the original sentence is very normal and idiomatic.

Yes. You can front it:

• Før jeg har læst det sidste kapitel i min roman, går jeg ikke i seng.

That is also correct.

When the subordinate clause comes first, the main clause still follows the Danish V2 rule, so the finite verb comes before the subject in the main clause:

• går jeg ikke i seng

This is a very useful pattern to notice in Danish word order.